Summary: Trapping of DNA in Nonuniform Oscillating Electric Fields
Charles L. Asbury and Ger van den Engh
Department of Molecular Biotechnology, University of Washington, Seattle, Washington 98195 USA
ABSTRACT DNA molecules can be manipulated in aqueous solution in a manner analogous to optical trapping. Due to the
induction of an electric dipole, DNA molecules are pulled by a gradient force to regions of high electric field strength.
Molecules can be locally trapped in an oscillating field using strips of very thin gold film to generate strong electric fields with
steep gradients. Spatial control over the trapped molecules is achieved because they are confined to a width of 5 m along
the edges of the gold-film strips. By mixing static and oscillating electric fields, trapped molecules can be moved from one
edge to another or made to follow precise trajectories along the edges. This phenomenon should be useful in microdevices
for manipulation of small quantities or single molecules of DNA.
INTRODUCTION
DNA molecules in solution carry a negative charge and
migrate toward the positive pole when placed in an electric
field. In addition to the net charge, the electric field induces
a dipole in the molecules. This dipole has few consequences
in the quasi-static, homogeneous electric fields that are
usually applied for electrophoresis of DNA. However, the
induced dipole becomes important when inhomogeneous
fields are used, because it renders the molecules sensitive to
field gradients. In a diverging electric field, the polarized